Hybrid Carrageenans Research Articles

Commercially available carrageenans show broad variation in their structure, composition, and functionality

Carrageenans are polysaccharides from red algae which are widely used as food additives and in other applications. Their structure is often described by different disaccharide repeating units, although it was already demonstrated that reality is more complex. In many studies, commercial carrageenans were used to establish structure function relationships, but a structural and compositional analysis was rarely conducted. Therefore, the aim of our study was to systematically and comprehensively characterize a broad collection of commercial carrageenans with different specifications from different manufacturers. For a more detailed characterization, an analytical approach based on partial enzymatic hydrolysis in combination with HPLC–MS and HPSEC-RI was developed and applied. Furthermore, rheology was used to gain detailed insights into the functionality of selected samples. Our results demonstrate that significant structural variation can be observed for commercial carrageenans. The samples contained different cations and the carrageenan type specified by the manufacturer did not always represent the structure of the corresponding polysaccharides. This was especially true for λ-carrageenans: Of the six commercial samples analyzed, none contained structural elements from the λ-type. Instead, the corresponding carrageenans contained κ-, ι- and ν-units. The application of the developed enzymatic-chromatographic approach showed that different hybrid carrageenans are present. In addition, the rheological analysis of the commercial carrageenan samples showed clear differences in the gelling properties upon calcium addition which could influence their behavior in different applications. Our results demonstrate that before an investigation of structure–function relationships, commercial carrageenan samples should be analyzed for their structure and composition. We also showed that the enzymatic-chromatographic approach described in this study is well suited for this purpose.

Viscoelastic Reversibility of Carrageenan Hydrogels under Large Amplitude Oscillatory Shear: Hybrid Carrageenans versus Blends.

The viscoelastic response of carrageenan hydrogels to large amplitude oscillatory shear (LAOS) has not received much attention in the literature in spite of its relevance in industrial application. A set of hybrid carrageenans with differing chemical compositions are gelled in the presence of KCl or NaCl, and their nonlinear viscoelastic responses are systematically compared with mixtures of kappa- and iota-carrageenans of equivalent kappa-carrageenan contents. Two categories of LAOS response are identified: strain softening and strain hardening gels. Strain softening gels show LAOS non-reversibility: when entering the nonlinear viscoelastic regime, the shear storage modulus G' decreases with increasing strain, and never recovers its linear value G0 after successive LAOS sweeps. In contrast to this, strain hardening carrageenan gels show a certain amount of LAOS reversibility: when entering the nonlinear regime, G' increases with strain and shows a maximum at strain γH. For strains applied below γH, G0 shows good reversibility and the strain hardening behavior is maintained. For strains larger than γH, G0 decreases significantly indicating an irreversible structural change in the elastic network. Strain hardening and elastic recovery after LAOS prevail for hybrid carrageenan and iota-carrageenan gels, but are only achieved when blends are gelled in NaCl, suggesting a phase separated structure with a certain degree of co-aggregated interface for mixed gels.

Biocatalytic Conversion of Carrageenans for the Production of 3,6-Anhydro-D-galactose.

Marine biomass stands out as a sustainable resource for generating value-added chemicals. In particular, anhydrosugars derived from carrageenans exhibit a variety of biological functions, rendering them highly promising for utilization and cascading in food, cosmetic, and biotechnological applications. However, the limitation of available sulfatases to break down the complex sulfation patterns of carrageenans poses a significant limitation for the sustainable production of valuable bioproducts from red algae. In this study, we screened several carrageenolytic polysaccharide utilization loci for novel sulfatase activities to assist the efficient conversion of a variety of sulfated galactans into the target product 3,6-anhydro-D-galactose. Inspired by the carrageenolytic pathways in marine heterotrophic bacteria, we systematically combined these novel sulfatases with other carrageenolytic enzymes, facilitating the development of the first enzymatic one-pot biotransformation of ι- and κ-carrageenan to 3,6-anhdyro-D-galactose. We further showed the applicability of this enzymatic bioconversion to a broad series of hybrid carrageenans, rendering this process a promising and sustainable approach for the production of value-added biomolecules from red-algal feedstocks.

To gel or not to gel – Tuning the sulfation pattern of carrageenans to expand their field of application

Carrageenans represent a major cell wall component of red macro algae and, as established gelling and thickening agents, they contribute significantly to a broad variety of commercial applications in the food and cosmetic industry. As a highly sulfated class of linear polysaccharides, their functional properties are strongly related to the sulfation pattern of their carrabiose repeating units. Therefore, the biocatalytic fine-tuning of these polymers by generating tailored sulfation architectures harnessing the hydrolytic activity of sulfatases could be a powerful tool to produce novel polymer structures with tuned properties to expand applications of carrageenans beyond their current use. To contribute to this vision, we sought to identify novel carrageenan sulfatases by studying several putative carrageenolytic clusters in marine heterotrophic bacteria. This approach revealed two novel formylglycine-dependent sulfatases from Cellulophaga algicola DSM 14237 and Cellulophaga baltica DSM 24729 with promiscuous hydrolytic activity towards the sulfated galactose in the industrially established ι- and κ-carrageenan, converting them into α- and β-carrageenan, respectively, and enabling the production of a variety of novel pure and hybrid carrageenans. The rheological analysis of these enzymatically generated structures revealed significantly altered physicochemical properties that may open the gate to a variety of novel carrageenan-based applications.

From Seaweeds to Hydrogels: Recent Progress in Kappa-2 Carrageenans.

Hybrid carrageenans, also called kappa-2 (K2) or weak kappa, are a class of sulfated polysaccharides with thermo-reversible gelling properties in water and are extracted from a specific family of red seaweeds. K2 are known in the industry for their texturizing properties which are intermediate between those of kappa-carrageenans (K) and iota-carrageenans (I). As such, K2 are gaining industrial interest, as they can replace blends of K and I (K + I) in some niche applications. Over the last decade or so, some progress has been made in unravelling K2's chemical structure. The understanding of K2 gel's structure-rheological properties' relationships has also improved. Such recent progress is reported here, reviewing the literature on gelling K2 published since the last review on the topic. The focus is on the seaweeds used for extracting K2, their block copolymer chemical structures, and how these impact on the gel's formation and rheological properties. The outcome of this review is that additional rheological and structural studies of K2 hydrogels are needed, in particular to understand their viscoelastic behavior under large deformation and to unravel the differences between the texturizing properties of K2 and K + I.

Native hybrid carrageenans from Sarcopeltis skottsbergii and Sarcothalia crispata: The role of counterions on their gelling properties

Carrageenans are red seaweed polysaccharides of great importance as gelling agents in the food texture market. The hybrid kappa/iota-carrageenan is extracted from certain cold-water species and its unique properties have given rise to growing demand for this biopolymer. Gelation of these polysaccharides is affected by the valency and, sometimes, the identity of counterions. The main objectives of this work were to investigate the role of potassium and calcium ions on the gelation of the native hybrid carrageenans from Sarcopeltis skottsbergii and Sarcothalia crispata from the South American Atlantic coast, and to optimize the structural properties of these gels. Response surface methodology was used to analyze the effects of carrageenan concentration, salt concentration, and KCl:CaCl2 ratio, on the rheology, texture, syneresis after 50 % deformation, and color of these gels. Both native carrageenans presented high extraction yield (42.73 ± 0.20 g/100 g for S. skottsbergii and 20.43 ± 7.64 g/100 g for S. crispata) and formed either weak or strong gels upon the addition of salt. Carrageenan and salt concentrations increased gel strength, but also increased turbidity. Moreover, KCl fraction also increased gel strength, attributed to the predominance of the kappa diad in these carrageenans, whose gelation is favored by potassium ions. All samples showed syneresis after deformation, being minimized with higher carrageenan and salt contents. Optimal compositions predicted by the selected models to maximize gel strength and minimize syneresis and haze, were 1.13 % carrageenan, 0.39 M salt and a proportion of 0.85 KCl for S. skottsbergii, and 1.16 % carrageenan, 0.36 M salt and a proportion of 0.85 KCl for S. crispata. Predicted responses for these optimal compositions were in accordance with the observed responses. Considering the worldwide growing demand for kappa/iota-carrageenan in the food industry, S. skottsbergii and S. crispata from the South Atlantic represent a potential source of these biopolymers.

Dark treatment effect on the carrageenan characterization in a red alga, Chondrus crispus

Carrageenan is a type of polysaccharides found in some seaweed species called carrageenophytes and is an essential compound in various pharmaceutical, food and cosmeceutical products. Alkali treatment is an industrial extraction method of carrageenan to improve gel quality. This method, however, has disadvantages, including producing effluents and decreasing gel yield. This study is to optimize the dark treatment duration of Chondrus crispus which is known to be an eco-friendly alternative to the alkali treatment for gel quality and yield improvements of hybrid carrageenans. In the 20-day dark treatment, yield and gel strength of carrageenan were significantly higher than control. The gel strength at the 20-day dark treatment was similar to that of alkali treatment. Sulfate content decreased as the gel strength increased. These results suggest that a dark treatment can be an alternative extraction method for carrageenan in C. crispus replacing the alkali treatment.

Exploring relationships between seaweeds carrageenan contents and extracted hybrid carrageenan properties in wild and cultivated Mastocarpus stellatus, Chondrus crispus and Ahnfeltiopsis devoniensis.

The types and amounts of carrageenans present in a set of Mastocarpus stellatus, Chondrus crispus and Ahnfeltiopsis devoniensis, are assessed by solid-state NMR performed directly on dried and powdered seaweeds. The resulting chemical analysis is compared with the chemical structure and gel elasticity of the hybrid carrageenans extracted from these three carrageenophytes. ν-carrageenan is only found in a single sample of M. stellatus, whereas C. crispus and A. devoniensis essentially contain ι- and μ-carrageenans. A significant amount of κ-carrageenan is found in all samples of M. stellatus, whereas this type of carrageenan was found in a single sample of A. devoniensis. Hybrid carrageenans (HK) made of κ-, ι-, μ- and ν-carrageenan units were found in all hot extracts from the seaweeds, and their respective contents are in line with earlier reports on the HK extracted from these seaweeds. No correlations between the carrageenan contents in eight seaweeds and the chemical structures of their corresponding extracted HK can be found. However, a positive nonlinear correlation between the intrinsic viscosity of extracted HK and their gel elastic modulus is found in a set of 8 carrageenophytes.

Green Extraction of Carrageenans from Mastocarpus stellatus.

The recovery of biopolymers from natural resources using eco-friendly extraction technologies that enhance their mechanical properties has gained attention in recent years. In this context, this work deals with the isolation of hybrid carrageenans from Mastocarpus stellatus red seaweed using subcritical water extraction operating in a wide range of thermal conditions (70–190 °C). The extracted biopolymers were analyzed by means of either Fourier-Transform infrared, nuclear magnetic resonance, rheological or cell viability assays. In parallel, the fundamental chemical composition of the seaweed used as raw material, as well as the main phytochemical properties of the soluble liquid extracts, were also studied. Results indicated that thermal extraction conditions significantly affected the rheological behavior of the recovered hybrid carrageenans. The hybrid carrageenan extraction yields varied, with results between 10.2 and 30.2% being the highest values obtained at hydrothermal treatment of 130 °C. A wide palette of viscous features was identified for recovered hybrid carrageenans, with the strongest rheology properties observed at the same temperature. It should be remarked that the maximum inhibitory effect was also obtained at 130 °C for both the ovarian carcinoma cell line (A2780) (65%, IC50: 0.31 mg/mL) and lung carcinoma cell line (A549) (59%, IC50: 0.41 mg/mL).

Chondrus crispus treated with ultrasound as a polysaccharides source with improved antitumoral potential

Ultrasound-assisted extraction was used to recover gelling biopolymers and antioxidant compounds from Chondrus crispus with improved biological potential. The optimal processing conditions were evaluated using a Box-Behnken design, and the impact on the biological and thermo-rheological properties of the carrageenan fraction and on the bioactive features of the soluble extracts were studied. The optimum extraction parameters were defined by extraction time of ~34.7 min; solid liquid ratio of ~2.1 g/100 g and ultrasound amplitude of ~79.0% with a maximum power of 1130 W. The dependent variables exhibited maximum carrageenan yields (44.3%) and viscoelastic modulus (925.9 Pa) with the lowest gelling temperatures (38.7 °C) as well as maximum content of the extract in protein (22.4 mg/g), gallic acid (13.4 mg/g) and Trolox equivalents antioxidant capacity (182.4 mg TEAC/g). Tested hybrid carrageenans exhibited promising biological activities (% of growth inhibition around 91% for four human cancer cellular lines: A549; A2780; HeLa 229; HT-29).

Valorisation of the industrial hybrid carrageenan extraction wastes using eco-friendly treatments

The goal of this paper is the valorisation of the Chondrus crispus (Rhodophyta) wastes generated during the industrial extraction of hybrid carrageenan using microwave technology of a temperature range from 140 to 200 °C, using water as a solvent. Mineral and phenolic content, antioxidant capacity and thermorheological features of the recovered hybrid carrageenans were determined. Results indicated the suitability for the recovery of high valuable compounds from these algae residues, after the optimization of the extraction conditions. At microwave processing conditions (160 °C, 5 min), it is still possible to recover around 10% of semi-refined hybrid carrageenan from the industrial raw material as well as to achieve the maximum value of total phenolic compounds of 12.8 mg GAE/g extract and antioxidant capacity of 51.70 mg Trolox/g extract. Extracted biopolymers exhibited thermomechanical features, in terms of viscoelastic moduli or gelling and melting temperatures, comparable to their commercial counterparts.

Formulation and Thermomechanical Characterization of Functional Hydrogels Based on Gluten Free Matrices Enriched with Antioxidant Compounds

Native starch from potatoes and hybrid carrageenans from the red alga Mastocarpus stellatus have been used as gluten-free gelling matrices to obtain functional hydrogels. The enrichment of gelling matrices with antioxidant compounds from natural sources is an increasing market trend. In this context, this work is aimed at the formulation and thermo-rheological characterization of functional hydrogels using potato starch from agro-industrial waste and kappa–iota hybrid carrageenans extracted from the above seaweed, enriched with antioxidant compounds from different agro-industrial products, such as waste coming from the pruning of green tea and two varieties of hops used in the brewing industry. Environmentally friendly technologies such as microwave hydrodiffusion and gravity, microwave-assisted extraction, ultrasounds and autohydrolysis were used for the recovery of antioxidant compounds. The results point out that functional hydrogels based on potato starch and hybrid carrageenans with a wide range of viscoelastic features can be achieved, with the particularity of being suitable for people with celiac disease. The incorporation of selected antioxidant extracts from vegetable by-products involved the drop (about tenfold) of the viscous and elastic properties of the formulated gels. The sequential combination of the above treatments could even further expand the thermo-rheological properties of formulated hydrogels, with potential application in functional foodstuffs and novel gluten-free goods.

The microwave assisted extraction sway on the features of antioxidant compounds and gelling biopolymers from Mastocarpus stellatus

Microwave assisted water extraction of hybrid carrageenan and antioxidant compounds from Mastocarpus stellatus red alga was first proposed to recover biopolymers with specific rheological properties, saving time, avoiding chemicals and enhancing extraction yields when compared with conventional treatments. The hybrid carrageenans, precipitated from the liquid fractions recovered after microwave assisted water extraction were analyzed by Fourier transform infrared attenuated total reflectance, high-performance size-exclusion chromatography and rheology. The corresponding soluble extracts were also characterized by total phenolic content, antioxidant capacity, proteins, sulfate and carbohydrate content. The highest phenolic, antioxidant capacity and sulfate content were observed at 190 °C, without notable effect of heating time between 3 and 6 min. In contrast, a clear impact of both microwave heating temperature and time on the molecular weight distribution of hybrid carrageenans as well as on the viscoelastic behavior of formulated hydrogels was identified, being the strongest hydrogels achieved at 170 °C for 6 min. It should be highlighted that all proposed hydrogels exhibited stable mechanical properties in the absence of syneresis for a month of cold storage, except those made with biopolymers obtained with the mildest extraction conditions (3 min at 70 °C).

A concise review of the red macroalgae Chondracanthus teedei (Mertens ex Roth) Kützing and Chondracanthus teedei var. lusitanicus (J.E. De Mesquita Rodrigues) Bárbara & Cremades

Chondracanthus teedei is a small red alga, whose fronds are cartilaginous membranous, dark crimson to red black, turning yellow-green due to decay. The main frond axes, due to their broad branches, reach 1 cm in the oldest portions in the case of the lusitanicus variety. Originally described in Portugal, C. teedei is found widespread in the Atlantic, Mediterranean, Black Sea and Indian Ocean. This cosmopolitan species is typical of lower intertidal and shallow subtidal habitats, of sciophilous habitats in semi-exposed or protected areas, and tolerates the presence of mud and sand. Its composition may vary according to the geographical location of origin, and the time of year when it is collected. It has relatively high levels of protein (14.66%), ash (28.68%), fibres (2.21%), lipids (1.82%) and moisture (86.73%), making this alga able to be considered for its implementation as food. In addition, C. teedei var. lusitanicus produces hybrid carrageenans belonging to the lambda family (xi-theta hybrid carrageenans), in the case of tetrasporophytes, and kappa-iota-mu-nu hybrid carrageenans, in the case of female gametophytes and non-fruited thalli. The carrageenans extracted from this species have antifungal and antiviral activities, and the dry ground biomass of C. teedei has potential to be used in cosmetic formulations.

Tailoring hybrid carrageenans from Mastocarpus stellatus red seaweed using microwave hydrodiffusion and gravity

This work deals with the use of microwave hydrodiffusion and gravity (MHG) for the recovery of hybrid carrageenans with specific mechanical features together with bioactive compounds. For this purpose, Mastocarpus stellatus red seaweed was used as raw material and the most adequate MHG processing conditions were studied. The physicochemical properties of the algae and the corresponding biopolymers, the fundamental characterisation of the bioactive compounds from the extracts (antioxidant capacity, sulfate content, protein content, among others) and the rheological features of the formulated gels were analysed. Results indicated that MHG is an adequate technique for obtaining functional extracts with potential applications in the food and non-food fields. Hybrid carrageenans with a wide range of viscoelastic features were recovered by MHG, saving time compared to conventional methods. The yields obtained for the recovered hybrid carrageenans and bioactive fractions were comparable to those obtained in red algae with conventional techniques.

Structure-rheological properties relationships in model drilling fluids formulated in aqueous solutions of carrageenan with varying chemical structures

Water-based drilling fluids (WDF) formulated with hybrid carrageenans (HY) recently showed attractive rheological and filtration properties, but the role of HY chemical structure on such WDF characteristics could not be established. Here, model drilling fluids were prepared by suspending sodium activated bentonite in two HY aqueous solutions, in order to assess relationships between the polysaccharide chemistry and the rheological-structural properties of the fluids. The rheological analysis of HY solutions indicates that the more sulfated HY is in coil conformation, whereas the other forms helices. The less sulfated HY promotes the slow build-up of a more elastic bentonite gel showing a larger yield stress, due to a less flocculated structure. A similar microscopic structure is achieved with the more sulfated HY, but a weaker gel is formed. In this suspension, the strain hardening behavior indicates that elasticity is ruled by flocs internal structure. Wide angle X-ray diffraction suggests that the weaker bentonite floc elasticity is related with a smaller number of bentonite lamellae in the aggregating stacks within the flocs. Overall, the set of results suggests that the carrageenan chemistry modulates the gel viscoelasticity by tuning the bentonite suspension structure at different length scales, from inter bentonite stacks to inter flocs distances.

Testing carrageenans with different chemical structures for water-based drilling fluid application

The hypothesis that the content in sulfate group (DS) on polysaccharide chains actually drives both viscoelastic and filtration properties of water-based drilling fluids (WBF) is tested by comparing the performances of fluids formulated with different carrageenans. Two hybrid carrageenans with different DS were purposely extracted from sustainably cultivated seaweeds. The rheological characterization of their solutions in 0.5 mol/L NaCl showed that these polysaccharides do not form helices under concentration and salt conditions used in WBF formulations. WBF containing the more sulfated carrageenan showed the best filtration properties, and its viscous attributes were only surpassed by a WBF formulated with a commercial mixture of less sulfated carrageenans showing helical conformers. This study shows that, for carrageenans, DS drives the WBF filtration properties. However, more complex bentonite-polysaccharide interactions and the presence of aggregating helical conformers seem to affect the WBF rheology.

Hybrid carrageenans as beer wort fining agents

Pure Na+ forms of furcellaran (β/κ-hybrid carrageenan), κ-carrageenan, κ/ι-hybrid carrageenan, ι-carrageenan and a hybrid carrageenan mix (made up of κ-, ι-, λ- and ν-carrageenans) were tested as beer wort fining agents. To find out which of the used carrageenans are the best beer wort clarifiers and whether they are prone to overdosage, polysaccharides with varying concentrations and molecular weights were tested. The polysaccharides were characterized by 1H NMR spectroscopy and size-exclusion chromatography. The fining efficiency of the tested polysaccharides was measured nephelometrically. Ultrasonicated and alkali treated carrageenan preparations were tested as beer wort fining agents and compared to the native samples. Undegraded furcellaran, κ-carrageenan and κ/ι-hybrids were efficient in lowering the turbidity of various beer worts, but the addition of ι-carrageenan and the carrageenan mix caused the turbidity to rise above the unfined sample value. Compared to the degraded samples, native galactans were more effective in lowering the beer wort turbidity. Higher concentrations of ultrasonicated carrageenans are needed to clarify the beer wort to similar turbidity values. Alkali treated carrageenans were more efficient beer wort fining agents compared to the native samples.

Air drying modelling of Mastocarpus stellatus seaweed a source of hybrid carrageenan

Water sorption isotherms from 5 up to 65 °C and air drying kinetics at 35, 45 and 55 °C of Mastocarpus stellatus seaweed were determined. Experimental sorption data were modelled using BET and Oswin models. A four-parameter model, based on Oswin model, was proposed to estimate equilibrium moisture content as function of water activity and temperature simultaneously. Drying experiments showed that water removal rate increased significantly with temperature from 35 to 45 °C, but at higher temperatures drying rate remained constant. Some chemical modifications of the hybrid carrageenans present in the seaweed can be responsible of this unexpected thermal trend. Experimental drying data were modelled using two-parameter Page model (n, k). Page parameter n was constant (1.31 ± 0.10) at tested temperatures, but k varied significantly with drying temperature (from 18.5 ± 0.2 10−3 min-n at 35 °C up to 28.4 ± 0.8 10−3 min-n at 45 and 55 °C). Drying experiments allowed the determination of the critical moisture content of seaweed (0.87 ± 0.06 kg water (kg d.b.)−1). A diffusional model considering slab geometry was employed to determine the effective diffusion coefficient of water during the falling rate period at different temperatures.

Structural and compositional characteristics of hybrid carrageenans from red algae Chondracanthus chamissoi

Two polysaccharides CCC and CCH were extracted from red algae Chondracanthus chamissoi by cold water and hot water, respectively. Characterization of the structure by chemical and spectroscopic methods showed that CCC was a hybrid carrageenan composed of κ-carrageenan (35%) and ι-carrageenan (43%) along with its precursor μ-carrageenan (22%) and CCH was an ideal κ-carrageenan. Oligosaccharides from CCH and CCC were prepared and their structural sequences determined by ES-CID-MS/MS gave further insight into the structural characteristics of hybrid carrageenans from C. chamissoi. Some hybrid oligosaccharides, e.g., κ–κ, κ–μ and κ–ι, were obtained with mild acid hydrolysis of CCC. Then, a regular even-numbered oligosaccharides generated with reductive acid hydrolysis of CCH confirmed it an ideal κ-carrageenan.